JP-2012-177303A (US2012/0216783A1) describes that a controller relates to a fuel injector injecting fuel by a lift-up (open-valve operation) of the valve body according to an electromagnetic force (suction force) generated by an energization of a coil. An opening time point of the valve body and an opening time period are controlled by controlling an energization start time point of the coil and an energization time period of the coil, and then an injection start time point and an injection amount are controlled.
As shown in FIG. 6, a voltage apply of the coil is continued from a time point that the energization of the coil is started to a time point that a coil current reaches a target peak value Ipeak. The target peak value represents a necessary value for opening the valve body.
When the valve body is opened, a current for holding this opening state is less than the target peak value. Specifically, when the suction force is increased, the suction force is affected by inductance due to a large variation in magnetic field. When the suction force is held to a specified value, the suction force is not affected by inductance.
Thus, at a time point that the coil current reaches the target peak value, a duty control applies voltage to the coil to decrease the coil current so that the coil current is held to a holding value Ihold which is less than the target peak value.
According to the duty control, as shown in FIG. 6, the suction force is increased synchronously with an increase in coil current. Thus, the valve body is opened. After the coil current reaches the target peak value, the suction force is decreased synchronously with a decrease in coil current. In this case, the coil current is decreased to the holding value Ihold.